This invention relates to an antenna for mobile satellite communication on a substantially horizontally oriented conductive base surface having substantially linear conductor parts, and an antenna connection point. Antennas of this type are known from German Patent 4,008,505.8. This antenna has crossed horizontal dipoles with dipole halves which are inclined downward in the form of a vee. It also has linear conductor parts, and the dipoles are mechanically fixed to one another at an angle of 90 degrees. They are attached at the upper end of a linear vertical conductor, fastened on a horizontally oriented conductive base surface.
To generate the circular polarization usually needed in satellite communications, the two horizontal dipoles, inclined downwardly in the form of a vee are electrically interconnected via a 90 degree phase network. Depending on satellite communications system, a steady antenna gain of 3 dBi for circular polarization is strictly required for satellite antennas in the elevation angle range of between 25 or 30 degrees, and 90 degrees. With antennas of this design, the antenna gain required in the region of the zenith angle can generally be achieved without problems. In contrast, the required antenna gain in the region of low elevation angles of 20 to 30 degrees can be achieved only with difficulty. Because the horizontal dipoles are inclined downwardly in the form of a vee, and require a sufficiently large distance from the conductive base surface in order to function, the required antenna gain cannot be obtained with a very low overall height of the antennas, as would be necessary for mobile service.
It is further known that curved antennas can be used to satisfy the gain requirements both in the angle range of low elevation, and in the case of high-angle radiation from linear conductors. The antenna form used frequently today is the quadrifilar helix antenna according to Kilgus (IEEE Transactions on Antennas and Propagation, 1976, pp. 238-241). These antennas often have a length of several wavelengths, and are not known as flat antennas with a low overall height. Even with an antenna of low overall height specified in European Patent 0952625 A2, the aforesaid gain values in the angle range of low elevation cannot be achieved.
An object of the invention is to provide an antenna which ensures that the ratio of antenna gain in the low elevation region to antenna gain in the zenith angle region can be adjusted as required in an azimuthal main plane, so that by combination of a plurality of these antennas, a directional diagram having the gain requirements for satellite communication with circularly polarized waves can be constructed, and the antenna has an electrically small overall height.
Antennas according to the invention can be made particularly simply and thus inexpensively, especially in their embodiment for satellite communications. Furthermore, by virtue of the fact that they are constructed above a conductive base surface, and that they can be configured with a low overall height, they are suitable particularly for service on vehicles. A further advantage is that they can be expanded to combination antennas for terrestrial communication, and this design provides a savings in overall space on motor vehicles. A further advantage is that measures can be taken to ensure that, in the event of any discontinuities that may be present in the conductive base surface or in the inclination thereof relative to the horizontal, which can occur due to the pitch or edge of a roof, the resulting perturbation of the directional diagram can be largely compensated.